The present invention is directed to an optical system that includes a coupling for efficiently transmitting, with minimum loss, light between a single fiber light guide and multiple single fiber light guides.
Large core optical fibers have been used recently in many applications, including architectural lighting, remote illuminations, and decorative lighting. Such fibers generally have a round cross-sectional shape and consist of a single highly transparent core material that is covered with a cladding formed of a material having a lower refractive index than that of the core, such that light can be guided along the length of the fiber. One problem in implementing many of the practical applications for such large core fibers is the inability to efficiently provide multiple fiber outputs from a single fiber input, or light source, or vice versa. Various light coupling schemes have been developed and implemented, and most suffer from either nonuniform splitting of the light energy amongst the output fibers, excessive losses, or both.
For example, a common method for splitting the light energy from a single input fiber into multiple output fibers is shown in FIGS. 1 and 2. A bundle 10 of individual output fibers 12 is constructed, and the beam of an input fiber or illuminator is input to the leading ends 16 of the bundled fibers 12. As shown in FIG. 1, due to the round cross-sectional shape of the individual fibers 12, interfiber gaps 14 are formed between adjacent fibers in the bundle 10. Due to the circular cross-sectional shape of the fibers, such interfiber gaps 14 are unavoidable and are usually filled with epoxy to hold the individual fibers 12 together in the bundle 10. Thus, the gaps 14 do not contribute to light transmission and therefore constitute a light energy loss.
In addition, as shown in FIG. 2, the input beam available at the output of an illuminator or at the end of an input fiber is normally not uniform in its intensity profile, as represented by the profile curve designated xe2x80x9cA.xe2x80x9d Accordingly, it can be appreciated that the amount of light coupled into the various output fibers 12 will vary from fiber to fiber. The amount of light in output 1 can be substantially different from that of output 2, depending on the intensity profile A of the input beam and the relative locations of outputs 1 and 2.
Another method for coupling light between one single fiber light guide and multiple single fiber light guides is described in U.S. Pat. No. 5,857,041. The apparatus described in the ""041 patent uses multiple lenses in a lens array that is constructed such that the full cross-section of the input beam is covered with lenses. Each individual lens corresponds to one output fiber. In the device shown in the ""041 patent, while the mismatch between the output area of the input fiber and the input area of the combined output fibers can be small, the addition of the lenses introduces extra Fresnel reflection losses and aberrations, thus decreasing the brightness of the transmitted light. Furthermore, the output of each fiber can also be different depending on the input intensity distribution of the light.
U.S. Pat. No. 5,341,445 describes an arrangement for coupling light from a light source to a plurality of output fibers using a polygonal-shaped coupler such that the output intensity profile of the input fiber is uniform. Accordingly, the output power from fiber to fiber is uniform. Although the output power is uniform from fiber to fiber, the efficiency is low due to the spaces between the output fibers as described above.
Accordingly, a need exists for an optical system having a coupling for transmitting light between one single fiber light guide and multiple single fiber light guides that avoids losses due to interfiber gaps and also avoids fiber to fiber output power variations due to the non-uniformity of the input light intensity profile.
An optical system includes a first coupler having a first transmitting section comprising a single fiber light guide, a first interface surface that has a polygonal cross-sectional shape, and a first transition section connecting the first transmitting section and the first interface surface and having a cross-sectional shape that varies smoothly from the cross-sectional shape of the first transmitting section to the cross-sectional shape of the first interface surface. The system also includes a second coupler having two or more single fiber light guides, each of the single fiber light guides including a second transmitting section, a second interface surface that has a polygonal cross-sectional shape, and a second transition section connecting the second transmitting section and the second interface surface and having a cross-sectional shape that varies smoothly from the cross-sectional shape of the second transmitting section to the cross-sectional shape of the second interface surface. The first coupler is in optical communication with the second coupler. The two or more single fiber light guides of the second coupler are arranged in mutual, lateral juxtaposition with the second interface surfaces thereof operatively positioned to transmit light to or from the first interface surface of the first coupler and with minimal gaps between adjacent ones of the second interface surfaces of the two or more single fiber light guides. The second interface surfaces of the two or more single fiber light guides of the second coupler have a combined cross-sectional area is substantially equal to a cross-sectional area of the first interface surface of the first coupler, so that the first interface surface is substantially covered by the second interface surfaces of the two or more single fiber light guides of the second coupler.
Light from a single input fiber optically coupled to the first transmitting section of the first coupler can be transmitted into the second coupler and divided into multiple output fibers optically coupled to the second transmitting sections of the second coupler. Alternatively, light from multiple input fibers optically coupled to the second transmitting sections of the second coupler can be coalesced into a single output fiber coupled to the first transmitting section of the first coupler.
The polygonal cross-sectional shape of the fist interface surface of the first coupler creates a more uniform intensity distribution, thus transmitting more uniform amounts of light to each single fiber of the second coupler. The polygonal cross-sectional shape of the second interface surfaces of the second coupler permits the two or more single fiber light guides of the second coupler to be arranged with little or no interfiber gap between adjacent light guides. Moreover, because the second interface surfaces substantially cover the first interface surface, transmission between the first and second interface surfaces can occur with little or no loss.
Other objects, features, and characteristics of the present invention will become apparent upon consideration of the following description and the appended claims with reference to the accompanying drawings, all of which form a part of the specification, and wherein like reference numerals designate corresponding parts in the various figures.